Timeline Jump Distance Change
In User Preferences (Ctrl+Alt+U), go to the Input section. In the search field on the right, search for shift up arrow (be sure to set your Filter Type from Name to Key Binding). You'll find the binding for the Frame Offset operator. If you expand the operator, you should see a Delta setting in the lower right. It's default value is 10. You can change it to 12 (or whatever other value you want).